It is sometimes said that humans are unlike other animals in at least one crucial respect. We do not simply form beliefs, desires and other mental states, but are capable of caring about our mental states in a distinctive way. We can care about the justification of our beliefs, and about the desirability of our desires. This kind of observation is usually made in discussions of free will and moral responsibility. But it has profound consequences, or so I shall argue, for our conception of the very nature of beliefs and other mental states. Suitably developed, it allows us to draw a line between two distinct ways in which a creature may possess a belief, represent a scene, and fall into error. The first way (which I shall call the 'm...